sound object research

The smallest sound that a person can hear, known as the threshold of hearing,

acoustic wave propagation

A sound wave is a vibration that travels through the air and through
>objects. When a wave reaches a surface of an object, some of the wave is
>reflected and some passes through into the object. Normally, very little of
>the wave remains within the object for very long. When the wave vibrates at
>a rate natural to the object, much of the wave remains within the object.
>As more waves like this enter the object, vibration builds up enough to
>distort or break the object.

http://www.newton.dep.anl.gov/askasci/phy00/phy00092.htm

http://science.howstuffworks.com/humans-hear-in-space1.htm

http://www.hibberts.co.uk/tuning.htm